Aquarium Calculators | Estimative Index | DIY Aquarium Plant Food Calculator
An Estimative index calculator to guide you to the correct dosing for your aquarium size. Stay algae free with this classic, cheap fertiliser method!
Estimative Index, Aquarium Calculator, dosing, fertiliser
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Estimative Index

The Estimative Index method of dosing is now known as a classic way of feeding your aquarium plants while maintaining an algae free environment.
Banishing the Nitrate/Phosphate/Algae correlation myth once and for all, it provides a ‘eutrophic’ solution in which nutrients are no longer the limiting factor in plant growth – shifting the emphasis towards lighting, CO2 and flow.

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  1. Grams or millilitres give a better resolution but spoons / cups might be more convenient. Normal domestic (kitchen) scales may not be accurate for small quantities.
    In this instance millilitres is being used as a volumetric measurement – i.e. 1 Teaspoon = 5ml
  2. If you wish to add more GH Boost to increase GH do it at water change.
  3. If you are making stock solutions and choose less than the suggested dose, all the salts may not dissolve.
    Try increasing the dose. If you have started your mix you could double the values for dose rate and stock volume.
  4. Values of ppm are added values. Actual Ca and Mg levels may be higher depending on your water hardness.
  5. The dose of trace elements is calculated with Fe as a proxy. Ppm values for micros are only true for the selected trace mix.

Above all, remember – This is an Estimative Index……and plants can’t read 😉

  • Derek
    Posted at 12:16h, 10 April Reply

    Do you use exactly 500ml of water for the stock solution? Or do you take into consideration the volume the powders take up and only fill the water up to the 500ml mark with the powders already added?

  • Nigel
    Posted at 08:43h, 11 April Reply

    Start with about 380ml, add salts – fully dissolve – top up to 500ml 🙂

  • galdadi
    Posted at 05:21h, 04 October Reply

    how do you do your ghost boost? Should I use calcium chloride and magnesium sulfate, and if so how many grams?
    I have a 300 liter tank. Thanks

    • Nigel
      Posted at 07:59h, 04 October Reply

      Any of the better shops in the Supplies section will sell it.
      There’re some notes on GH and how to increase it on James’ Planted Tank too.

  • Stuart
    Posted at 11:27h, 17 May Reply

    Can this work over a two week cycle? Ie do a 50% water change every 14 days. If so how to dose?


    • Nigel
      Posted at 14:19h, 17 May Reply

      Yes you could. You’d just need to reduce your lighting so you can lower your CO2 demand. This would allow the plants to grow more slowly over the 2 weeks.
      The water change is dependant on plant metabolites etc rather than dosing, so you could leave that as it is – however as you’d be running a lower energy system you could dose less to save money.


  • Marcel
    Posted at 00:53h, 29 November Reply

    With what kind of fertiliser are you adding the sulphur? As far as I know there is no sulpher added with the mentioned components. I am using for example Potassium Sulfate.

    • Nigel
      Posted at 07:08h, 29 November Reply

      Hi Marcel, the Sulphur comes from the Sulphate in Potassium Sulphate (K2SO4

      • Kutay
        Posted at 19:12h, 15 February Reply

        But there is no Potassium Sulphate in the dosing routine provided above ?

        • Nigel
          Posted at 07:07h, 16 February Reply

          There’s no need for Potassium Sulphate

  • Kutay
    Posted at 19:10h, 15 February Reply

    As far as I see from the dosing schedule, only KNO3 and KH2PO4 are added, Where is Magnesium ?

    • Nigel
      Posted at 07:07h, 16 February Reply

      If you need to raise your Hardness the magnesium and Calcium come from your GH Booster.

  • David
    Posted at 23:23h, 05 September Reply

    For “Tank Volume” in the calculator and/or dosing instructions… if i have a 120 gal tank do i base the dosing off the stated tank volume? Or do you take into consideration that due to substrate, driftwood, rocks, etc. you may only have 100 gal of actual water? Thanks.

    • Nigel
      Posted at 07:26h, 06 September Reply

      Stated tank volume 🙂

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